Dental impression trays are widely known and used to produce impressions of sections of patient's dentition or the entire upper or lower portion of the dentition. The known process involves placing impression material into the impression tray and then inserting the tray into the patient's mouth to create the impression. The doctor maneuvers or manipulates the tray within the patients mouth relative to the teeth until the appropriate position is achieved and thereafter holds the tray in this position. The impression material cures while it is inside the mouth. Once completed, the doctor removes the cured impression from the patient's mouth after which it is used to create restorations.
Impression trays which are presently used typically are made of a combination of a mouthpiece and a handle. These devices are usually arcuate in shape to fit the contours of a patient's mouth. Moreover, the mouthpieces typically comprise an inner and outer wall and a base. The outer walls also have apertures which allow the impression material to escape during impressioning.
Recent trays even contain reservoirs in the base to allow the displaced impression material to be extruded during impressioning. These reservoirs are created by placing perpendicular slits underneath holes in the base of the tray. Thus, the reservoir is created by forming a cavity beneath the holes in the base of the tray. An example of a reservoir, as is typically used in presently known impression trays, is shown in U.S. Pat. No. 5,336,086. The purpose for these reservoirs is to allow displaced impression material to escape and to provide an interlock during impressioning. However, these devices generally fail to create a sufficient interlock to securely hold the impression material to the impression tray. That is, displaced material which is extruded as a rod through the holes in the base into the reservoirs, thus, when the displaced material cures or hardens, it generally retains the vertical rod like form. The absence of a means to properly position the displaced material beneath the holes in the base can result in the material hardening in a form which will not secure the material beneath the base in the reservoir. In which case, the intended interlock fails and subsequently the impression material does not hold securely to the impression tray.
As shown in FIG. 8, presently used trays also contain straight ribs on the surface of the base which are intended to provide a more rigid tray. However, the alignment and positioning of these ribs can fail to adequately prevent patients' teeth from abutting the base of the tray. That is, presently used trays typically use straight ribs which are perpendicular to the inner and outer walls of the tray.
Furthermore, presently used trays also have holes in the inner wall of the tray. However, holes in the inner walls of presently used trays do not always adequately secure or attach excess impression material which has flowed thereto. Instead, as presently used, the holes in the inner walls of trays can sometimes serve merely to allow excess material to escape the tray and be extruded into the patients' mouth. That is, absent a means to assist the holes in the base in displacement of excess material which is extruded through them, the holes do not adequately secure hardened impression material which has flowed through. Thus, holes in the inner walls as presently used can not only fail to function as intended but can cause further discomfort to the patient.
The known prior art trays also contain a plate, extending across the palate of the patient, integral with or attached to the tray used to make impressions of the upper dentition. When the tray is inserted into the patient's mouth, the plate makes contact with the upper portion of the patient's mouth including the soft palate. Applying pressure to the soft palate in the upper portion of the patient's mouth with the plate of the prior art tray can induce a patient's gag reflex thereby causing severe discomfort for the patient. Furthermore, the possibility of inducing the patient's gag reflex limits the maneuverability of the tray by the doctor.
From the foregoing it will be understood that the currently used impression material does not adhere well to the plastic surface of the tray, largely due to the typical finish on the surface of the molded plastic article. Accordingly, a prior practice has been to coat the tray with bonding agent which adheres the impression material to the tray. Unfortunately, the bonding agent is toxic and extreme caution must be taken to avoid excess exposure to the patient. Therefore, the use of common bonding agents is expected to be banned.
Thus, an impression tray is needed which provides a solution to the aforementioned problems and thereby provides improvements in the formation of dental restorations.